给一个01的矩阵，相邻的1可以分成1组组成一个建筑物，问有多少个建筑物
dfs:

```cpp
#include<stdio.h>
#include<iostream>
#include<algorithm>
#define MAXN_ROW 100
#define MAXN_COL 100
using namespace std;
int dx[4] = { 0,0,-1,1 };
int dy[4] = { -1,1,0,0 };
int map[MAXN_ROW][MAXN_COL];
bool vis[MAXN_ROW][MAXN_COL];
void dfs(int i, int j)     //dfs访问第i行第j列的点
{
	vis[i][j] = 1;
	for (int k = 0; k < 4; k++)
	{
		int newx = i + dx[k];
		int newy = j + dy[k];
		if (map[newx][newy] != 0 && vis[newx][newy]==0)
		{
			dfs(newx, newy);
		}
	}
}
int main()
{
	int m, n;
	int cnt = 0;
	scanf("%d%d", &m, &n);
	for (int i = 0; i < m; i++)
	{
		for (int j = 0; j < n; j++)
		{
			scanf("%d", *(map + i) + j);
		}
	}
	for (int i = 0; i < m; i++)
	{
		for (int j = 0; j < n; j++)
		{
			if (map[i][j] == 1)
			{
				if (vis[i][j] == 0)
				{
					dfs(i, j);
					cnt++;
				}
				
			}
		}
	}
	printf("%d\n", cnt);
	return 0;
}